Photosensitive resin composition, method of forming level difference pattern using the photosensitive resin composition, and method of producing ink jet head

ABSTRACT

To provide a positive type photosensitive resin composition, containing at least an acrylic resin having a carboxylic anhydride structure in a molecule, and a compound that generates an acid when irradiated with light.

TECHNICAL FIELD

The present invention relates to a photosensitive resin composition thatcan be suitably used in producing an ink jet head for generating arecording liquid droplet for use in an ink jet recording method. Thepresent invention also relates to: a method of forming a leveldifference pattern and a method of producing an ink jet head each usingthe photosensitive resin composition; and an ink jet head produced bythe method of producing an ink jet head.

BACKGROUND ART

An ink jet head applicable to an ink jet recording method (liquiddischarge recording method) involving discharging a recording solutionsuch as ink to carry out recording is generally equipped with: an inkflow path; a liquid discharge energy generating portion placed in partof the ink flow path; and a fine ink discharge port (called an“orifice”) for discharging ink in the ink flow path by means of energyfrom the liquid discharge energy generating portion. Examples of amethod of producing such an ink jet head conventionally include:

-   (1) a production method involving: perforating an element substrate    on which heaters for generating thermal energy for discharging a    liquid, a driver circuit for driving those heaters, and the like are    formed with through holes for ink supply; forming a pattern serving    as an ink flow path wall by means of a negative type resist; and    bonding a plate on which an ink discharge port is formed by means of    electroforming or excimer laser processing to the pattern; and-   (2) a method involving: preparing an element substrate formed in the    same manner as in the above production method; processing a resin    film (in general, polyimide is suitably used) to which an adhesive    layer is applied with excimer laser to form an ink flow path and an    ink discharge port; and attaching the processed ink flow path    structure plate and the element substrate to each other under heat    and pressure.

In the ink jet head produced according to each of the productionmethods, in order to enable fine ink droplets for high-image-qualityrecording to be discharged, a distance between a heater affecting adischarge amount and a discharge port must be as short as possible. Toachieve this, the height of the ink flow path must be reduced, or thesize of: a discharge chamber, which becomes part of the ink flow path,as a bubble generating chamber in contact with the liquid dischargeenergy generating portion; or the discharge port must be reduced. Thatis, the ink flow path structure to be laminated on the substrate must bemade thin in order to enable the head produced according to each of theabove methods to discharge a fine ink droplet. However, it is extremelydifficult to process a thin ink flow path structure plate with highaccuracy before the plate is attached to a substrate.

To solve the problems in those production methods, JP-B 06-45242discloses a method of producing an ink jet head (also referred to as acasting method) involving: patterning a mold of an ink flow path bymeans of a photosensitive material on a substrate on which a liquiddischarge energy generating element is formed; applying and forming acoating resin layer on the substrate to cover the mold pattern; forming,in the coating resin layer, an ink discharge port in communication withthe mold of an ink flow path; and removing the photosensitive materialused for the mold. In the method of producing a head, a positive typeresist is used as the photosensitive material because the resist can beeasily removed. According to the production method, an ink flow path, adischarge port, and the like can be formed extremely finely withextremely high accuracy because photolithography for a semiconductor isapplied.

However, after the ink flow path pattern has been formed by means of thepositive type resist, the positive type resist is coated with a negativetype resist to form a discharge port. Therefore, when lightcorresponding to the absorption wavelength region of the negative typeresist is applied, the pattern formed by means of the positive typeresist is irradiated with the light having the wavelength region. As aresult, a decomposition reaction or the like of the positive type resistmaterial is promoted, with the result that inconvenience may occur.Furthermore, the negative type resist is applied onto the ink flow pathpattern formed by means of the positive type resist, so there may ariseproblems such as the dissolution and deformation of the ink flow pathpattern upon application of the negative type resist.

JP-A 2004-42650 and JP-A 2004-46217 each disclose a photo-degradableresin having a carboxylic anhydride structure as a positive type resistmaterial capable of avoiding the above problems.

Meanwhile, a structure has been investigated for making an ink jet headthinner and for increasing the performance of the head, in which adischarge port is arranged above a discharge pressure generating elementplaced on a substrate, and the shape of an ink flow path incommunication with the discharge port is changed in the height directionof the substrate. With regard to a change in shape of an ink flow pathin the height direction of a substrate, JP-A 10-291317 discloses that,in excimer laser processing of an ink flow path structure, the opacityof a laser mask is partially changed to control the processing depth ofa resin film, so a change in shape of an ink flow path inthree-dimensional directions, that is, in-plane directions parallel withan element substrate and the height direction of the element substrateis realized.

JP-A 2004-46217 cited above also discloses a method involving: creatinga mold constituting a part serving as an ink flow path by means of apositive type resist in a two-layer structure; patterning each of theupper layer and the lower layer into a desired shape to change the shapeof an ink flow path in the height direction of a substrate.

In the method of producing an ink jet head using the casting methoddescribed above, investigation has been made to solve each of thefollowing problems in additionally increasing production efficiency.

-   (1) Problem with regard to the sensitivity and photosensitive    wavelength of a positive type photosensitive resin composition

In an acrylic resin having an acid anhydride structure in a positivetype photosensitive resin composition disclosed in each of JP-A2004-42650 and JP-A 2004-46217 cited above, a decomposition reactionprogresses by virtue of energy absorbed by a carbonyl group, so lighthaving a relatively short wavelength region must be used and theselectivity of the wavelength of light to be applied is narrow. For thisreason, when a mold constituting a part serving as an ink flow path hasa two-layer structure, a positive type photosensitive resin compositionto be combined with the mold can be selected from only a narrow range,so the degree of freedom of design for increasing production efficiencyand reducing a production cost is low.

In addition, in additionally increasing efficiency in a productionprocess for a mold constituting a part serving as an ink flow path, acomposition with increased sensitivity has been required.

-   (2) RE: process efficiency in forming an ink flow path the shape of    which changes in a height direction from a substrate to a discharge    port

In a method involving the use of laser processing described above,control in a depth direction in the laser processing can be conducted inprinciple. However, excimer laser used for such processing, which isdifferent from excimer laser used for exposure of a semiconductor, islaser having high brightness in a wide bandwidth. Therefore, it is verydifficult to stabilize laser illuminance while suppressing a fluctuationin illuminance in a plane to be irradiated with laser. In particular, ina high-image-quality ink jet head, unevenness in discharge property dueto a fluctuation in processed shape between discharge nozzles isobserved as image unevenness, so the realization of an increase inprocessing accuracy is of great concern. Furthermore, in many cases, aminute pattern cannot be formed owing to a taper attached to a plane tobe processed with laser/

On the other hand, when a mold constituting a part serving as an inkflow path is made of a positive type resist and has a two-layerstructure, in order to selectively pattern each of the upper layer andthe lower layer, the photosensitive wavelength of the upper layer andthe photosensitive wavelength of the lower layer are separated from eachother in such a manner that an exposing condition of the one layer doesnot affect that of the other layer. In addition, 2 exposing deviceshaving different irradiation wavelengths must be used for selectivelyseparating exposure wavelengths as described above. Only one exposingdevice can separate an irradiation wavelength by means of an opticalfilter, in which case an expensive optical filter is needed.Furthermore, the absorption wavelength ends of the respective materialpartly overlap. Therefore, in order to prevent the lower layer resistfrom reacting when exposing the upper layer resist to light, the upperlayer resist must be exposed to light after light having a wavelengthregion in which the upper layer resist originally reacts is partly cut.In such a case, a reduction in sensitivity often occurs.

Even in the case where the wavelength region of light to be applied tothe upper layer is the same as that of light to be applied to the lowerlayer, or the wavelength regions partly overlap, the upper layer and thelower layer are allowed to be selectively patterned, that is, anexposing condition for the patterning of the upper layer is preventedfrom affecting the lower layer, so a problem in a device structureoccurring when the exposure wavelengths are selectively separated can besolved, and an additional increase in efficiency of a production processcan be achieved.

Furthermore, when a mold constituting a part serving as an ink flow pathhas a two-layer structure, an applying step must be performed at leasttwice and a prebaking step must be performed at least twice, resultingin an increase in number of steps. If a process having a reduced numberof steps can be selected, production efficiency can be increased byselecting the process having a reduced number of steps depending onprocess design.

DISCLOSURE OF THE INVENTION

The present invention has been made for solving each of the problemsdescribed above, and an object of the present invention is to expand arange of selection of photosensitive wavelength while increasing theexposure sensitivity of a positive type photosensitive resin compositionusing an acrylic resin having a carboxylic anhydride structure. Anotherobject of the present invention is to provide: a method of forming apattern with which an ink flow path the shape of which changes in aheight direction from a substrate to a discharge port can be formed withhigh accuracy and high efficiency by means of a positive typephotosensitive resin composition; and a method of producing an ink jethead using the same.

The present invention includes each of the following inventions.

According to one aspect of the present invention, there is provided apositive type photosensitive resin composition, containing at least: (1)an acrylic resin having a carboxylic anhydride structure in a molecule;and (2) a compound that generates an acid when irradiated with light.

According to another aspect of the present invention, there is provideda method of forming a pattern having a level difference on a substrateby means of a positive type photosensitive resin, including: (1) a stepof forming a layer of the above photosensitive resin composition on thesubstrate; (2) a first photolithographic step of removing a part excepta part serving as a first pattern of the layer of the photosensitiveresin composition up to a predetermined depth in a thickness directionto form the first pattern composed of a part protruding from thepredetermined depth; and (3) a second photolithographic step of removinga part on the substrate except a part serving as a second pattern of thelayer of the photosensitive resin composition on which the first patternis formed while maintaining the shape of the first pattern to prepare apattern having a level difference shape in which the first pattern isplaced on the second pattern, characterized in that: the firstlithography step includes process steps of exposure, heating afterexposure, and development; a reaction for making the layer of thephotosensitive resin composition positive in the first photolithographicstep is derived from at least a hydrolytic reaction of a carboxylicanhydride in the acrylic resin; the second photolithographic stepincludes process steps of exposure and development; and a reaction formaking the layer of the photosensitive resin composition positive in thesecond photolithographic step is derived from at least a main chaindecomposition reaction of the acrylic resin.

According to another aspect of the present invention, there is provideda method of producing an ink jet head including: a discharge port fordischarging ink; an ink flow path which is in communication with thedischarge port and has therein a pressure generating element fordischarging the ink; a substrate on which the pressure generatingelement is formed; and an ink flow path forming member which is joinedto the substrate to form the ink flow path, the method including thesteps of: (1) arranging a layer of a positive type photosensitive resincomposition on the substrate on which the pressure generating element isformed; (2) irradiating a predetermined site of the layer of thephotosensitive resin composition with ionization radiation; (3) removingthe site irradiated with the ionization radiation through development toform a desired ink flow path pattern; (4) forming, on the ink flow pathpattern, a coating resin layer for forming an ink flow path wall; (5)forming, in the coating resin layer placed on the pressure generatingelement formed on the substrate, an ink discharge port; and (6)dissolving and removing the ink flow path pattern, characterized in thatthe positive type photosensitive resin composition is the abovephotosensitive resin composition.

According to another aspect of the present invention, there is provideda method of producing an ink jet head including: a discharge port fordischarging ink; an ink flow path which is in communication with thedischarge port and has therein a pressure generating element fordischarging the ink; a substrate on which the pressure generatingelement is formed; and an ink flow path forming member which is joinedto the substrate to form the ink flow path, the method including thesteps of: (1) arranging a layer of a first positive type photosensitiveresin on the substrate on which the pressure generating element isformed; (2) forming a layer of a second positive type photosensitiveresin on the layer of the first positive type photosensitive resin; (3)irradiating a predetermined site of the layer of the second positivetype photosensitive resin with ionization radiation having a wavelengthregion in which the layer of the second positive type photosensitiveresin can react; (4) removing the site of the layer of the secondpositive type photosensitive resin irradiated with the ionizationradiation through development to form a second ink flow path pattern;(5) irradiating a predetermined site of the layer of the first positivetype photosensitive resin with ionization radiation having a wavelengthregion in which the layer of the first positive type photosensitiveresin can react; (6) removing the site of the layer of the firstpositive type photosensitive resin irradiated with the ionizationradiation through development to form a first ink flow path pattern; (7)forming, on the first and second ink flow path patterns, a coating resinlayer for forming an ink flow path wall; (8) forming, in the coatingresin layer placed on the pressure generating element formed on thesubstrate, an ink discharge port; and (9) dissolving and removing thefirst and second ink flow path patterns, characterized in that thesecond positive type photosensitive resin is the above photosensitiveresin composition.

According to another aspect of the present invention, there is provideda method of producing an ink jet head including: a discharge port fordischarging ink; an ink flow path which is in communication with thedischarge port and has therein a pressure generating element fordischarging the ink; a substrate on which the pressure generatingelement is formed; and an ink flow path forming member which is joinedto the substrate to form the ink flow path, the method including: (1) astep of forming a layer of the above photosensitive resin composition onthe substrate on which the pressure generating element is formed; (2) afirst photolithographic step of removing a part except a part serving asa first ink flow path pattern of the layer of the photosensitive resincomposition up to a predetermined depth in a thickness direction to formthe first ink flow path pattern composed of a part protruding from thepredetermined depth; (3) a second photolithographic step of removing apart on the substrate except a part serving as a second ink flow pathpattern of the layer of the photosensitive resin composition on whichthe first ink flow path pattern is formed while maintaining the shape ofthe first ink flow path pattern to prepare a level difference structurein which the first ink flow path pattern is placed on the second inkflow path pattern; (4) a step of forming, on the level differencestructure, a coating resin layer for forming an ink flow path wall; (5)a step of forming, in the coating resin layer placed on the pressuregenerating element formed on the substrate, an ink discharge port; and(6) a step of dissolving and removing the level difference structure,characterized in that: the first lithography step includes process stepsof exposure, heating after exposure, and development; a reaction formaking the layer of the photosensitive resin composition positive in thefirst photolithographic step is derived from at least a hydrolyticreaction of a carboxylic anhydride in the acrylic resin; the secondphotolithographic step includes process steps of exposure anddevelopment; and a reaction for making the layer of the photosensitiveresin composition positive in the second photolithographic step isderived from at least a main chain decomposition reaction of the acrylicresin.

According to another aspect of the present invention, there is providedan ink jet head produced according to any one of the above methods ofproducing an ink jet head.

The positive type photosensitive resin composition of the presentinvention has high sensitivity and can reduce a processing time in apattern formation process. Furthermore, according to the presentinvention, a high-accuracy ink jet head which enableshigh-speed-and-high-image-quality printing can be produced by means of asimple method with high efficiency and in high yield. In addition,according to the present invention, a level difference pattern useful inproducing such an ink jet head can be formed with high accuracy and highefficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a substrate.

FIG. 2 is a sectional view of the substrate on which an ink dischargepressure generating element is formed.

FIG. 3 is a sectional view of the substrate on which a layer of aphotosensitive resin composition is formed.

FIG. 4 is a sectional view of the substrate on which a flow path patternis formed.

FIG. 5 is a sectional view of the substrate on which a nozzleconstitution member is formed.

Fig. β is a sectional view of the substrate on which an ink repellentagent layer is formed.

FIG. 7 is a sectional view of the substrate on which an ink dischargeport is formed.

FIG. 8 is a sectional view of the substrate on which an etching mask isformed.

FIG. 9 is a sectional view of the substrate on which an ink supply portis formed.

FIG. 10 is a sectional view of a complete ink jet head.

FIG. 11 is a sectional view of a substrate.

FIG. 12 is a sectional view of the substrate on which an ink dischargepressure generating element is formed.

FIG. 13 is a sectional view of the substrate on which a first positivetype resist layer is formed.

FIG. 14 is a sectional view of the substrate on which a second positivetype resist layer is formed.

FIG. 15 is a sectional view of the substrate on which a second flow pathpattern is formed.

FIG. 16 is a sectional view of the substrate on which a first flow pathpattern is formed.

FIG. 17 is a sectional view of the substrate on which a nozzleconstitution member is formed.

FIG. 18 is a sectional view of the substrate on which an ink repellentagent layer is formed.

FIG. 19 is a sectional view of the substrate on which an ink dischargeport is formed.

FIG. 20 is a sectional view of the substrate on which an etching mask isformed.

FIG. 21 is a sectional view of the substrate on which an ink supply portis formed.

FIG. 22 is a sectional view of a complete ink jet head.

FIG. 23 is a sectional view of a substrate.

FIG. 24 is a sectional view of the substrate on which an ink dischargepressure generating element is formed.

FIG. 25 is a sectional view of the substrate on which a positive typeresist layer is formed.

FIG. 26 is a sectional view of the substrate on which a first flow pathpattern is formed.

FIG. 27 is a sectional view of the substrate on which a second flow pathpattern is formed.

FIG. 28 is a sectional view of the substrate on which a nozzleconstitution member is formed.

FIG. 29 is a sectional view of the substrate on which an ink repellentagent layer is formed.

FIG. 30 is a sectional view of the substrate on which an ink dischargeport is formed.

FIG. 31 is a sectional view of the substrate on which an etching mask isformed.

FIG. 32 is a sectional view of the substrate on which an ink supply portis formed.

FIG. 33 is a sectional view of a complete ink jet head.

FIG. 34 is a graph showing a relationship between an amount of aphotoacid generator to be added and a developable film thickness.

FIG. 35 is a graph showing a relationship between a PEB temperature anda developable film thickness.

BEST MODE FOR CARRYING OUT THE INVENTION

The positive type photosensitive resin composition to be used in thepresent invention contains at least: (1) an acrylic resin having acarboxylic anhydride structure in a molecule; and (2) a compound thatgenerates an acid when irradiated with light. The photosensitive resincomposition causes 2 kinds of reactions for making positive: a reactionfor making positive derived from hydrolysis due to a so-called chemicalamplification reaction and a reaction for making positive derived from amain chain decomposition reaction of an acrylic main chain. In theformer reaction for making positive, the carboxylic anhydride structurein the acrylic resin structure undergoes a hydrolytic reaction under anacid condition to significantly improve solubility with respect to analkali solution. That is, a cation produced and diffused by performinglight irradiation and post exposure bake (PEB) by using a photoacidgenerator causes the hydrolysis of the carboxylic anhydride structure inthe resin to produce a carboxylic acid, thereby improving solubilitywith respect to an alkali developer. As a result, the photosensitiveresin composition can be used as a high-sensitivity positive typeresist. In addition, in the latter reaction for making positive, a mainchain having a carbon-carbon bond produced by radical polymerization ofa vinyl group in the acryl monomer is cleaved by a so-called Norrishtype reaction to reduce its molecular weight, so it can be easilydissolved into a solvent. For this reason, when a wavelength for actinga photoacid generator is set to a region in which the main chaindecomposition reaction of an acrylic resin also occurs, the main chaindecomposition reaction of the acrylic resin can be advanced in additionto the hydrolytic reaction of the carboxylic anhydride structure, so aphotosensitive resin composition with additionally high sensitivity canbe obtained. That is, a reduction in molecular weight derived from themain chain decomposition reaction of the acrylic resin, and a change inpolarity and a reduction in molecular weight due to hydrolysis advancein tandem, so the sensitivity is extremely high.

When the photosensitive resin composition is used for producing an inkjet head, the photosensitive resin composition has, for example, anadvantage in that a distance between a discharge-energy generatingelement (such as a heater) and an orifice (discharge port) andpositional accuracy of the element with respect to the center of theorifice, one of the important factors affecting head properties, can beeasily realized. That is, the thickness of a layer obtained by applyingthe positive type photosensitive resin composition according to thepresent invention can be strictly controlled with high reproducibilityby means of a thin film coating technique conventionally used.Therefore, the distance between the discharge energy generating elementand the orifice can be easily set. In addition, alignment between thedischarge energy generating element and the orifice can be performedoptically by means of a photolithographic technique. As a result,alignment can be performed with dramatically high accuracy as comparedto a method that has been conventionally used for producing a liquiddischarge recording head, the method involving bonding an ink flow pathstructure plate to a substrate.

On the other hand, in the case where a mold constituting a part servingas an ink flow path is formed into a structure having 2 layers eachcomposed of a positive type photosensitive resin composition, the upperlayer is constituted by the positive type photosensitive resincomposition according to the present invention having high sensitivityand the lower layer is constituted by a positive type photosensitiveresin composition having low sensitivity relative to the positive typephotosensitive resin composition according to the present invention toset a light intensity or amount of exposure at the time of exposure ofthe upper layer to a low value in accordance with the high-sensitivityphotosensitive resin composition constituting the upper layer. In thiscase, the lower layer having lower sensitivity than that of the upperlayer is not sensitized at the time of exposure of the upper layer. Thatis, an exposing condition of the upper layer does not affect the lowerlayer. In this case, the upper layer and the lower layer may have thesame photosensitive wavelength (wavelength region), the photosensitivewavelengths of the layers may partly overlap, or the photosensitivewavelengths may be completely separated from each other. In the casewhere positive type photosensitive resin compositions having the samephotosensitive wavelength are used, the positive type photosensitiveresin compositions are preferably selected in such a manner that thedifference between the sensitivities of the upper layer and the lowerlayer is at least 5 times, or preferably 10 or more times.

The positive type photosensitive resin composition according to thepresent invention can also be suitably used for a method involving:forming a single layer of a positive type photosensitive resincomposition on a substrate; forming a first pattern on the surfacelayer; and forming the entire layer into a second pattern whilemaintaining the first pattern. In particular, the positive typephotosensitive resin composition according to the present invention canadjust the film thickness to be developed by controlling the amount of aphotoacid generator to be added and a PEB condition as described later.Therefore, a precise first pattern can be formed up to a predetermineddepth with high accuracy. In particular, in the case of a head having afurther shortened distance between a discharge pressure generatingelement and a discharge port, the thickness of a mold constituting apart serving as an ink flow path is also set to be extremely small, sothe formation of a first pattern requires high accuracy particularly ina depth direction. When a positive type photosensitive resin compositioncausing only a single reaction for making positive is used, it isdifficult to form a minute first pattern with high accuracy with noeffect on a residual image layer part for forming a second pattern. Onthe other hand, the photosensitive resin composition according to thepresent invention can control the height of a first pattern by adjustingthe amount of a photoacid generator to be added and a PEB condition. Asa result, patterning can be performed with high accuracy.

An acrylic resin to be incorporated into the positive typephotosensitive resin composition according to the present invention hasa carboxylic anhydride structure in a molecule. Furthermore, the acrylicresin preferably has the carboxylic anhydride structure at a side chainthereof and preferably undergoes intramolecular cross-linking throughthe carboxylic anhydride structure from the viewpoint of solventresistance. To be specific, the acrylic resin preferably has at leastone kind of structural units represented by the following generalformulae 1 and 2.

(In the general formulae 1 and 2, Ri to R₄ each independently representa hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Ri and R₄each have the above meaning for each unit.) The acrylic resin can beproduced by radical polymerization of a methacrylic anhydride monomeralone or of the monomer and another acrylic monomer such as methylmethacrylate, ethyl methacrylate, propyl methacrylate, or isopropylmethacrylate by means of a conventionally known method. For example,when a copolymer of methacrylic anhydride and methyl methacrylate isused, the copolymerization ratio and molecular weight of the copolymercan be arbitrarily set. However, as a ratio of methacrylic anhydrideincreases, a gel component is apt to be produced during radicalpolymerization. In contrast, as the ratio of methacrylic anhydridereduces, the sensitivity as a resist tends to reduce. In view of theabove, methacrylic anhydride and methyl methacrylate are preferablycopolymerized at a methacrylic anhydride/methyl methacrylate ratio of 5mol /95 mol % to 30 mol %/70 mol %. In addition, a low molecular weighttends to result in poor film formability, while a high molecular weighttends to reduce sensitivity. Therefore, a weight average molecularweight (Mw) is preferably about 20,000 to 60,000.

In addition, a compound that generates an acid when irradiated withlight to be used in the present invention is not particularly limited.Preferable examples thereof include: aromatic sulfonium salts such asTPS-102, 103, 105, MDS-103, 105, 205, 305, DTS-102, 103 commerciallyavailable from Midori Kagaku Co., Ltd. and SP-170, 172 commerciallyavailable from ASAHI DENKA Co., Ltd.; aromatic iodonium salts such asDPI-105, MPI-103, 105, BBI-101, 102, 103, 105 commercially availablefrom Midori Kagaku Co., Ltd.; and triazine compounds such as TAZ-101,102, 103, 104, 105, 106, 107, 110, 111, 113, 114, 118, 119, 120commercially available from Midori Kagaku Co., Ltd. In addition, thecompound may be added in such amount as may provide target sensitivity.In particular, the compound can be suitably used in an amount in therange of 1 to 7 mass % with respect to the acrylic resin. For example,SP-100 commercially available from ASAHI DENKA Co., Ltd. may be added asa wavelength sensitizer as required.

A general-purpose solvent coat method such as spin coating or slitcoating is applicable to the formation of the layer of thephotosensitive resin composition. Although a bake temperature can bearbitrarily set, a heat treatment is performed preferably at 90° C. to280° C. for 1 minute to 120 minutes, or particularly preferably at 120°C. to 250° C. for 3 minutes to 60 minutes in order to impart sufficientsolvent resistance.

Next, each embodiment of a method of producing an ink jet head using thepositive type photosensitive resin composition according to the presentinvention (including a method of forming a level difference pattern)will be described.

EMBODIMENT 1

FIGS. 1 to 10 each schematically show the cross section of the structureof an ink jet head and a method of producing the same. First, asubstrate 1 as shown in FIG. 1 is prepared. The shape, material, and thelike of the substrate are not particularly limited as long as thesubstrate can function as part of an ink flow path constitution member,and can also function as a support for a material layer with which anink flow path and an ink discharge port to be described later areformed. In this example, a silicon substrate is used because an inksupply port penetrating through the substrate is formed by means ofanisotropic etching to be described later.

A desired number of ink discharge pressure generating elements 2 such asan electrothermal converting element and a piezoelectric element arearranged on the substrate 1 (FIG. 2). The ink discharge pressuregenerating elements 2 provide an ink liquid with discharge energy fordischarging ink liquid droplets, whereby recording is performed. Forexample, when electrothermal converting elements are used as the inkdischarge pressure generating elements 2, the elements heat a recordingsolution near them to cause a change in state of the ink, therebygenerating discharge energy. For example, when piezoelectric elementsare used, discharge energy is generated by the mechanical vibration ofthe elements.

Electrodes for inputting control signals (not shown) for operating theelements are connected to those discharge pressure generating elements2. In general, various functional layers such as a protective layer (notshown) for improving the durability of those discharge pressuregenerating elements 2 and an adhesion improving layer (not shown) forimproving adhesiveness between a nozzle constitution member to bedescribed later and the substrate are arranged. In the present inventionas well, those functional layers may be arranged with no problem.

Next, as shown in FIG. 3, a layer 3 of the photosensitive resincomposition according to the present invention is formed on thesubstrate 1 including the ink discharge pressure generating elements 2(FIG. 3), and the photosensitive resin composition is patterned througha series of photolithographic steps to form an ink flow path pattern 4(FIG. 4). A positive type resist is generally used because the ink flowpath pattern 4 must be dissolved and removed in a subsequent step. Thephotosensitive resin composition according to the present inventiondescribed above is used as the positive type resist.

To be specific, an application solution is prepared by dissolving thephotosensitive resin composition according to the present invention intoa solvent, and is applied to a predetermined site of the substrate anddried to form the layer 3 of the photosensitive resin composition. Abake treatment is performed as required, and then the resultant issubjected to: pattern exposure by means of UV irradiation equipment (notshown) through a photomask (not shown); and a PEB treatment by means ofa hot plate (not shown). Although a PEB condition may be arbitrarilyset, a heat treatment at 90 to 150° C. for about 1 to 5 minutes ispreferable. The light to which the layer of the photosensitive resincomposition of the present invention is exposed may be ionizationradiation such as a far ultraviolet ray, an X-ray, or an electron beamin addition to an ultraviolet ray.

Next, development is performed. Any developer can be used as long as thedeveloper can dissolve an exposed portion and hardly dissolves anunexposed portion. The inventors of the present invention have madeextensive studies to find that a developer containing: a glycol etherwhich can be mixed with water at an arbitrary ratio and has 6 or morecarbon atoms; a nitrogen-containing basic organic solvent; and water isparticularly suitably used. The glycol ether to be particularly suitablyused is at least one kind of ethylene glycol monobutyl ether anddiethylene glycol monobutyl ether, while the nitrogen-containing basicorganic solvent to be particularly suitably used is one containing atleast one kind of ethanolamine and morpholine. For example, a developerhaving the composition disclosed in JP-A 03-10089 is also suitably usedas a developer for polymethyl methacrylate (PMMA) used as a resist inX-ray photolithography in the present invention. For example, adeveloper having a composition ratio of the respective componentsdescribed above of 60 vol % of diethylene glycol monobutyl ether, 5 vol% of ethanolamine, 20 vol % of morpholine, and 15 vol % of ion-exchangedwater may be used. The preferable composition range of the developer issuch that the glycol ether which can be mixed with water at an arbitraryratio and has 6 or more carbon atoms accounts for 50 to 70 vol % whilethe nitrogen-containing basic organic solvent accounts for 20 to 30 vol% (the balance being ion-exchanged water).

As shown in FIG. 5, a nozzle constitution member 5 is formed by means ofa method such as spin coating, roll coating, or slit coating on thesubstrate 1 on which the flow path pattern 4 is formed. Here, the nozzleconstitution member 5 is preferably photosensitive because an inkdischarge port 7 to be described later can be easily formed with highaccuracy by photolithography. Such photosensitive coating resin isrequested to have high mechanical strength as a structural material,adhesiveness with a base, and ink resistance as well as resolution forpatterning a minute pattern of an ink discharge port. A cationicallypolymerizable epoxy resin composition can be suitably used as a materialsatisfying those properties.

Examples of an epoxy resin to be used in the present invention include,without limitation, a product having a molecular weight of about 900 ormore out of products of a reaction between bisphenol A andepichlorohydrin, a product of a reaction between bromo-containingbisphenol A and epichlorohydrin, a product of a reaction between phenolnovolac or o-cresol and epichlorohydrin, and a polyfunctional epoxyresin having an oxycyclohexane skeleton described in each of JP-A60-161973, JP-A 63-221121, JP-A 64-9216, and JP-A 02-140219.

A compound having an epoxy equivalent of preferably 2,000 or less, ormore preferably 1,000 or less is suitably used as the epoxy compound.This is because an epoxy equivalent in excess of 2,000 reduces across-linking density at the time of a curing reaction to cause problemsin terms of adhesiveness and ink resistance.

A compound that generates an acid when irradiated with light can be usedas a cationic photopolymerization initiator for curing the epoxy resin.For example, SP-150, SP-170, or SP-172 commercially available from ASAHIDENKA Co., Ltd. can be suitably used. An additive or the like may beappropriately added as required to the composition. For example, aflexibility imparting agent is added for the purpose of reducing theelasticity of the epoxy resin, or a silane coupling agent is added forobtaining additional adhesion with a base.

Next, an ink repellent agent layer 6 having photosensitivity is formedon the nozzle constitution member 5 (FIG. 6). The ink repellent agentlayer 6 can be formed by means of a coating method such as spin coating,roll coating, or slit coating. In this example, the nozzle constitutionmember 5 and the ink repellent agent layer 6 must not be compatible witheach other to a degree more than necessary because the layer 6 is formedon the uncured nozzle formation member 5.

Next, the resultant is subjected to pattern exposure through a mask (notshown) and to development to form an ink discharge port 7 (FIG. 7) Thenozzle constitution member 5 and the ink repellent agent layer 6 thathave been subjected to the pattern exposure are developed with anappropriate solvent, whereby the ink discharge port 7 can be formed asshown in FIG. 7. At this time, the flow path pattern 4 can be dissolvedand removed simultaneously with the development. However, in general,multiple heads are arranged on the substrate 1 and are used as ink jetheads after a cutting step. Therefore, the flow path pattern 4 ispreferably left for coping with waste generated at the time of cutting(waste generated at the time of cutting can be prevented from enteringthe flow path because the flow path pattern 4 remains), and the flowpath pattern 4 is preferably dissolved and removed after the cuttingstep.

Next, an ink supply port penetrating through the substrate 1 is formed.The ink supply port can be formed by means of anisotropic etchinginvolving the use of a resin composition having resistance to an etchantas an etching mask. A silicon substrate having <100> and <110> crystalorientations can have selectivity in a depth direction and a widthdirection with respect to the advancing direction of etching when it issubjected to alkali chemical etching, whereby anisotropy of etching canbe obtained. In particular, in a silicon substrate having a <100>crystal orientation, a depth to be etched is geometrically determineddepending on a width to be etched, so the depth to be etched can becontrolled. For example, a hole narrowing from an etching start surfacein a depth direction with an inclination of 54.7° can be formed.

As shown in FIG. 8, an etching mask 8 composed of a resin havingresistance to an etchant is formed on the rear surface of the substrate1. Then, the resultant is immersed for etching in an aqueous solution ofpotassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide, orthe like as an alkali etchant while the solution is heated, to therebyform an ink supply port 9 (FIG. 9). At this time, as described in, forexample, JP-A 2001-10070, for the purpose of preventing a defect such asa pin hole, a mask having a two-layer structure with a dielectric filmmade of silicon oxide, silicon nitride, or the like can be used with noproblem. The etching mask may be formed before the flow path pattern 4and the nozzle constitution member 5 are formed.

Next, after a cutting and separating step (not shown), the flow pathpattern 4 is dissolved and removed, and the etching mask 8 is removed asrequired. Furthermore, the remainder is subjected to a heat treatment asrequired to completely cure the nozzle constitution member 5 and the inkrepellent agent layer 6. After that, joining of a member for ink supply(not shown) and electrical joining for driving the ink dischargepressure generating elements (not shown) are performed to complete anink jet head (FIG. 10).

A liquid discharge head of the present invention can be produced byapplying the steps described above. A production method according to thepresent invention is performed by means of a solvent coat method such asspin coating used in a semiconductor production technique. Therefore, anink flow path having an extremely accurate height can be stably formed.In addition, a two-dimensional shape in a direction parallel with asubstrate can be formed with an accuracy of the order of submicronbecause a semiconductor photolithographic technique is used.

EMBODIMENT 2

FIGS. 11 to 22 each schematically show the cross section of thestructure of an ink jet head and a method of producing the same. First,a substrate 1 as shown in FIG. 11 is prepared. The shape, material, andthe like of the substrate are not particularly limited as long as thesubstrate can function as part of an ink flow path constitution member,and can also function as a support for a material layer with which anink flow path and an ink discharge port to be described later areformed. In this example, a silicon substrate is used because an inksupply port penetrating through the substrate is formed by means ofanisotropic etching to be described later.

A desired number of ink discharge pressure generating elements 2 such asan electrothermal converting element and a piezoelectric element arearranged on the substrate 1 (FIG. 12). The ink discharge pressuregenerating elements 2 provide ink with discharge energy for dischargingthe ink, whereby recording is performed. For example, whenelectrothermal converting elements are used as the ink dischargepressure generating elements 2, the elements heat ink near them to causea change in state of the ink, thereby generating discharge energy. Forexample, when piezoelectric elements are used, discharge energy isgenerated by the mechanical vibration of the elements.

Electrodes for inputting control signals (not shown) for operating theelements are connected to those discharge pressure generating elements2. In general, various functional layers such as a protective layer (notshown) for improving the durability of those discharge pressuregenerating elements 2 and an adhesion improving layer (not shown) forimproving adhesiveness between a nozzle constitution member to bedescribed later and the substrate are arranged. In the present inventionas well, those functional layers may be arranged with no problem.

Next, as shown in FIG. 13, a first positive type resist layer 11 isformed on the substrate 1 including the ink discharge pressuregenerating elements 2. A main chain decomposition-type positive typeresist generally available can be used as a first positive type resist.For example, polymethyl isopropenyl ketone (ODUR manufactured by TokyoOhka Kogyo Co., Ltd.), polymethyl methacrylate (PMMA), a methylmethacrylate-methacrylic acid copolymer, or the like can be used. Thelayer may be applied by means of a general-purpose solvent coat methodsuch as spin coating or slit coating. Although a bake temperature can bearbitrarily set, a heat treatment is performed preferably at 120° C. to280° C. for 1 minute to 120 minutes in order to impart sufficientsolvent resistance.

Next, a second positive type resist layer 12 is formed on the firstpositive type resist layer 11 (FIG. 14). The second positive type resistlayer 12 is formed of such photosensitive resin composition containingan acrylic resin having a carboxylic anhydride structure as describedabove. To be specific, an application solution is prepared by dissolvingthe photosensitive resin composition according to the present inventioninto a solvent, and is applied to the first positive type resist layer11 on the substrate and dried to form the second positive type resistlayer 12. A bake treatment is performed as required. The second positivetype resist layer 12 can be used as a high-sensitivity resist because,as described above, the hydrolysis of the carboxylic anhydride structureoccurs to produce a carboxylic acid, thereby improving solubility withrespect to an alkali developer. The high-sensitivity resist hassensitivity several ten to several hundred times as high as that of amain chain decomposition-type resist used for the first positive typeresist layer 11 such as polymethyl isopropenyl ketone, polymethylmethacrylate, or a methyl methacrylate-methacrylic acid copolymer.Therefore, even in the case where an upper layer resist is exposed tolight having a wavelength region in which a lower layer resist reacts,the upper layer resist can be patterned with no effect on the firstpositive type resist layer as the lower layer.

Furthermore, it is extremely difficult to arbitrarily set thephotosensitive wavelength of a general main chain decomposition-typepositive type resist as described above as a resist because the resistutilizes a Norrish type cleavage reaction, and the reaction is caused byenergy absorbed by carbonyl. For this reason, when a main chaindecomposition-type positive type resist is used for each of upper andlower layers, a combination of resist materials for the upper and lowerlayers is inevitably limited from the viewpoint of photosensitivewavelength. In contrast, the present invention provides an advantagethat the selectivity of a material for a lower layer expands. Inaddition, even when a photosensitive wavelength must be separated, thephotosensitive wavelength of an upper layer can be arbitrarily set byselecting a photoacid generator to be used for the upper resist.

Next, the resultant is subjected to: pattern exposure by means of UVirradiation equipment (not shown) through a photomask (not shown); PEBby means of a hot plate (not shown); and development (FIG. 15). Althougha PEB condition may be arbitrarily set, a heat treatment at 90 to 150°C. for about 1 to 5 minutes is preferable.

In addition, the same developer as that in Embodiment 1 can be used.

Next, after a heat treatment to be performed as required, the firstpositive type resist layer 11 is subjected to pattern exposure through aphotomask (not shown) and developed to form a first flow path pattern 14(FIG. 16). Any developer can be used as the developer for the firstpositive type resist layer 11 as long as the developer can dissolve anexposed portion and hardly dissolves an unexposed portion. Methylisobutyl ketone and such developer as described above are particularlypreferably used.

As shown in FIG. 17, a nozzle constitution member 5 is formed by meansof a method such as spin coating, roll coating, or slit coating on thesubstrate 1 on which a flow path pattern having a two-layer structurecomposed of the second flow path pattern 13 and the first flow pathpattern 14 is formed. Here, the nozzle constitution member 5 ispreferably photosensitive because an ink discharge port 9 to bedescribed later can be easily formed with high accuracy byphotolithography. Such photosensitive coating resin is requested to havehigh mechanical strength as a structural material, adhesiveness with abase, and ink resistance as well as resolution for patterning a minutepattern of an ink discharge port. The same cationically polymerizableepoxy resin composition as that in Embodiment 1 can be suitably used asa material satisfying those properties.

Next, an ink repellent agent layer 6 having photosensitivity is formedon the nozzle constitution member 5 (FIG. 18). The ink repellent agentlayer β can be formed by means of a coating method such as spin coating,roll coating, or slit coating. However, the nozzle constitution member 5and the ink repellent agent layer 6 must not be compatible with eachother to a degree more than necessary because the layer 6 is formed onthe uncured nozzle formation member 5. As described above, when acationically polymerizable chemical composition is used for the nozzleconstitution member 7, it is preferable to incorporate a cationicallypolymerizable functional group into the ink repellent agent layer 6having photosensitivity.

Next, the resultant is subjected to pattern exposure through a mask (notshown) and to development to form an ink discharge port 7 (FIG. 19). Thenozzle constitution member 5 and the ink repellent agent layer 6 thathave been subjected to the pattern exposure are developed with anappropriate solvent, whereby the ink discharge port 7 can be formed asshown in FIG. 19. At this time, the first and second flow path patternscan be dissolved and removed simultaneously with the development.However, in general, multiple heads are arranged on the substrate 1 andare used as ink jet heads after a cutting step. Therefore, the first andsecond flow path patterns are preferably left for coping with wastegenerated at the time of cutting (waste generated at the time of cuttingcan be prevented from entering the flow path because the flow pathpatterns remain), and the flow path patterns are preferably dissolvedand removed after the cutting step.

Next, an ink supply port penetrating through the substrate 1 is formed.The ink supply port can be formed by means of anisotropic etchinginvolving the use of a resin composition having resistance to an etchantas an etching mask. A silicon substrate having <100> and <110> crystalorientations can have selectivity in a depth direction and a widthdirection with respect to the advancing direction of etching when if issubjected to alkali chemical etching, whereby anisotropy of etching canbe obtained. In particular, in a silicon substrate having a <100>crystal orientation, a depth to be etched is geometrically determineddepending on a width to be etched, so the depth to be etched can becontrolled. For example, a hole narrowing from an etching start surfacein a depth direction with an inclination of 54.7° can be formed.

As shown in FIG. 20, an etching mask 8 composed of a resin havingresistance to an etchant is formed on the rear surface of the substrate1. Then, the resultant is immersed for etching in an aqueous solution ofpotassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide, orthe like as an alkali etchant while the solution is heated, to therebyform an ink supply port 9 (FIG. 21). At this time, as described in, forexample, JP-A 2001-10070, for the purpose of preventing a defect such asa pin hole, a mask having a two-layer structure with a dielectric filmmade of silicon oxide, silicon nitride, or the like can be used with noproblem. The etching mask may be formed before the flow path patternsand the nozzle constitution member are formed.

Next, after a cutting and separating step (not shown), the flow pathpatterns are dissolved and removed to form an ink flow path 10, and theetching mask 8 is removed as required. Furthermore, the remainder issubjected to a heat treatment as required to completely cure the nozzleconstitution member 5 and the ink repellent agent layer 6. After that,joining of a member for ink supply (not shown) and electrical joiningfor driving the ink discharge pressure generating elements (not shown)are performed to complete an ink jet head (FIG. 22).

As described above, a production method according to the presentinvention is performed by means of a solvent coat method such as spincoating used in a semiconductor production technique. Therefore, an inkflow path having an extremely accurate height can be stably formed. Inaddition, an ink flow path can be formed into a shape with an accuracyof the order of submicron because a semiconductor photolithographictechnique is used. Furthermore, the production method of the presentinvention provides a flow path pattern having a two-layer structure, soan ink discharge port can be formed into a convex shape. The convexshape has an increasing effect on an ink discharge speed and anincreasing effect on the direct advancing property of ink. Accordingly,an ink jet head capable of performing recording with increased imagequality can be provided.

EMBODIMENT 3

FIGS. 23 to 33 each schematically show the cross section of thestructure of an ink jet head and a method of producing the same. Inaddition, FIGS. 34 and 35 each show the sensitivity property of apositive type resist to be used in the present invention.

First, a substrate 1 as shown in FIG. 23 is prepared. The shape,material, and the like of the substrate are not particularly limited aslong as the substrate can function as part of a liquid flow pathconstitution member, and can also function as a support for a materiallayer with which an ink flow path and an ink discharge port to bedescribed later are formed. In this example, a silicon substrate is usedbecause an ink supply port penetrating through the substrate is formedby means of anisotropic etching to be described later.

A desired number of ink discharge pressure generating elements 2 such asan electrothermal converting element and a piezoelectric element arearranged on the substrate 1 (FIG. 24). The ink discharge pressuregenerating elements 2 provide ink with discharge energy for dischargingthe ink droplets, whereby recording is performed. For example, whenelectrothermal converting elements are used as the ink dischargepressure generating elements 2, the elements heat a recording solutionnear them to cause a change in state of the recording solution, therebygenerating discharge energy. For example, when piezoelectric elementsare used, discharge energy is generated by the mechanical vibration ofthe elements.

Electrodes for inputting control signals (not shown) for operating theelements are connected to those discharge pressure generating elements2. In general, various functional layers such as a protective layer (notshown) for improving the durability of those discharge pressuregenerating elements 2 and an adhesion improving layer (not shown) forimproving adhesiveness between a nozzle constitution member to bedescribed later and the substrate are arranged. In the present inventionas well, those functional layers may be arranged with no problem.

Next, as shown in FIG. 25, a positive type resist layer 15 is formed onthe substrate 1 including the ink discharge pressure generating elements2 (FIG. 25). Part of the positive type resist layer 15 is patterned in athickness direction in a first photolithographic step to form a firstflow path pattern 16 (FIG. 26). The positive type resist layer 15 isformed of the photosensitive resin composition according to the presentinvention described above.

Patterning is performed in the first photolithographic step by using thereaction for making positive derived from hydrolysis, to develop apredetermined thickness of the positive type resist layer 15 formed onthe substrate 1. Thus, the first flow path pattern 16 can be formed.After that, a second flow path pattern 17 is formed in a secondphotolithographic step to be described later by using the reaction formaking positive derived from a main chain decomposition reaction. Thus,an ink flow path pattern having a convex level difference can be formed.

Furthermore, an exposure wavelength in the first photolithographic stepand an exposure wavelength in the second photolithographic step may bedifferent for the purpose of preventing the main chain decompositionreaction of the positive type resist from progressing owing to theexposure wavelength in the first photolithographic step. In this case,the main chain decomposition reaction of an acrylic copolymer occursowing to light having a wavelength of 220 to 280 nm, so a compoundreacting with light having a wavelength of an i line (365 nm) or a gline (436 nm) is preferably used as a photoacid generator, and the firstphotolithographic step is preferably performed by means of a steppercorresponding to each wavelength.

A general-purpose solvent coat method such as spin coating or slitcoating is applicable to the formation of the positive type resist layer15. Although a bake temperature can be arbitrarily set, a heat treatmentis performed preferably at 90° C. to 280° C. for 1 minute to 120minutes, or particularly preferably at 120° C. to 250° C. for 3 minutesto 60 minutes in order to impart sufficient solvent resistance.Subsequent to the heat treatment, the resultant is subjected to: patternexposure by means of UV irradiation equipment (not shown) through aphotomask (not shown); and a PEB treatment by means of a hot plate (notshown). Although a PEB condition may be arbitrarily set, a heattreatment at 90 to 150°0 C. for about 1 to 5 minutes is preferable.

For reference purposes, FIG. 34 shows a graph of a developable filmthickness (PEB condition: 120° C.-180 seconds) when the addition amountof a photoacid generator (TPS-105 manufactured by Midori Kagaku Co.,Ltd.) is changed, while FIG. 35 shows a graph of a developable filmthickness (photoacid generator: TPS-105 manufactured by Midori KagakuCo., Ltd., addition amount: 3 wt %, PEB time: 180 seconds) when a PEBtemperature is changed. It is needless to say that the kind and additionamount of the photoacid generator, an amount of exposure, and a PEBtemperature and a PEB time can be arbitrarily set in such a manner thata desired film thickness can be developed.

Next, development is performed. The same developer as that in Embodiment1 can be used. Next, a remaining part without being developed in thefirst photolithographic step is patterned again in the secondphotolithographic step to form the second flow path pattern 17 (FIG.27). At this time, a postbake treatment may be performed before thesecond photolithographic step is performed. In this embodiment, thesurface layer of the remaining part without being developed at the timeof development in the first photolithographic step also contacts analkali developer. For this reason, a chemical amplification reaction ofthe remaining part is inhibited, and patterning is performed in thesecond photolithographic step by using the reaction for making positivederived from a main chain decomposition reaction described above.Accordingly, a reaction with relatively low sensitivity occurs. First,simultaneously with the first photolithographic step, the resultant issubjected to: pattern exposure by means of UV irradiation equipment (notshown) through a photomask (not shown); and development. Any developercan be used as long as the developer can dissolve an exposed portion andhardly dissolves an unexposed portion. The same developer as that usedin the first photolithographic step may be used. The amount of exposuremay be arbitrarily set in accordance with a remaining film thickness.

As shown in FIG. 28, a nozzle constitution member 5 is formed by meansof a method such as spin coating, roll coating, or slit coating on thesubstrate 1 on which the first and second flow path patterns are formedas described above. Here, the nozzle constitution member 5 is preferablyphotosensitive because an ink discharge port 7 to be described later canbe easily formed with high accuracy by photolithography. Suchphotosensitive coating resin is requested to have high mechanicalstrength as a structural material, adhesiveness with a base, and inkresistance as well as resolution for patterning a minute pattern of anink discharge port. The same cationically polymerizable epoxy resincomposition as that in Embodiment 1 can be suitably used as a materialsatisfying those properties.

Next, an ink repellent agent layer 6 having photosensitivity is formedon the nozzle constitution member 5 (FIG. 29). The ink repellent agentlayer 6 can be formed by means of a coating method such as spin coating,roll coating, or slit coating. However, in this example, the nozzleconstitution member 5 and the ink repellent agent layer 6 must not becompatible with each other to a degree more than necessary because thelayer 6 is formed on the uncured nozzle formation member 5.

Next, the resultant is subjected to pattern exposure through a mask (notshown) and to development to form an ink discharge port 7 (FIG. 30) Thenozzle constitution member 5 and the ink repellent agent layer 6 thathave been subjected to the pattern exposure are developed with anappropriate solvent, whereby the ink discharge port 7 can be formed asshown in FIG. 30. At this time, the flow path patterns can be dissolvedand removed simultaneously with the development. However, in general,multiple heads are arranged on the substrate 1 and are used as ink jetheads after a cutting step. Therefore, the flow path patterns arepreferably left for coping with waste generated at the time of cutting(waste generated at the time of cutting can be prevented from enteringthe flow path because the flow path patterns remain), and the flow pathpatterns are preferably dissolved and removed after the cutting step.

Next, an ink supply port penetrating through the substrate 1 is formed.The ink supply port can be formed by means of anisotropic etchinginvolving the use of a resin composition having resistance to an etchantas an etching mask. A silicon substrate having <100> and <110> crystalorientations can have selectivity in a depth direction and a widthdirection with respect to the advancing direction of etching when it issubjected to alkali chemical etching, whereby anisotropy of etching canbe obtained. In particular, in a silicon substrate having a <100>crystal orientation, a depth to be etched is geometrically determineddepending on a width to be etched, so the depth to be etched can becontrolled. For example, a hole narrowing from an etching start surfacein a depth direction with an inclination of 54.7° can be formed.

As shown in FIG. 31, an etching mask 8 composed of a resin havingresistance to an etchant is formed on the rear surface of the substrate1. Then, the resultant is immersed for etching in an aqueous solution ofpotassium hydroxide, sodium hydroxide, tetramethylammonium hydroxide, orthe like as an alkali etchant while the solution is heated, to therebyform an ink supply port 9 (FIG. 32). At this time, as described in, forexample, JP-A 2001-10070, for the purpose of preventing a defect such asa pin hole, a mask having a two-layer structure with a dielectric filmmade of silicon oxide, silicon nitride, or the like can be used with noproblem. The etching mask may be formed before the flow path patternsand the nozzle constitution member are formed.

Next, after a cutting and separating step (not shown), the flow pathpatterns are dissolved and removed, and the etching mask 8 is removed asrequired. Furthermore, the remainder is subjected to a heat treatment asrequired to completely cure the nozzle constitution member 5 and the inkrepellent agent layer 6. After that, joining of a member for ink supply(not shown) and electrical joining for driving the ink dischargepressure generating elements (not shown) are performed to complete anink jet head (FIG. 33).

The liquid discharge head of the present invention can be produced byapplying the steps described above. According to the production methodaccording to the present invention, an ink flow path having a convexlevel difference can be stably formed with extremely high accuracy. Inaddition, a two-dimensional shape in a direction parallel with asubstrate can be formed with an accuracy of the order of submicronbecause a semiconductor photolithographic technique is used.

In each of the figures to which reference is made to in the respectiveexamples, an ink jet head having 2 orifices (discharge ports) is shown.It is needless to say that the same holds true for a high-densitymultiafray ink jet head having 3 or more orifices.

Hereinafter, specific examples will be described.

EXAMPLE 1

(1) Synthesis of a Methacrylic Anhydride/Methyl Methacrylate-Copolymer.

400 g of cyclohexanone were charged into a flask equipped with astirring device and a reflux pipe, and the temperature was held at 103to 105° C. in an oil bath. A mixture of 5.41 g (0.053 mol) ofmethacrylic anhydride, 48.6 g (0.468 mol) of methyl methacrylate, 2.40 g(0.015 mol) of AIBN, and 100 g of cyclohexanone was dropped into theflask over 2 hours, followed by a polymerization reaction for 3 hours.After that, the reaction solution was charged into hexane to precipitateand collect the powder of a methacrylic anhydride/methyl methacrylatecopolymer. The resultant copolymer had a weight average molecular weight(Mw: in terms of polystyrene) of 30,000 and a degree of dispersion(Mw/Mn) of 3.3.

(2) Preparation of a Positive Type Resist

30 g of the resultant copolymer were dissolved into 70 g ofcyclohexanone, and 1.5 g of triphenylsulfonium antimonate (TPS-103manufactured by Midori Kagaku Co., Ltd.) were added to and dissolvedinto the solution. After that, the solution was filtered through a0.2-μm membrane filter to prepare a positive type resist solution.

(3) Production of an Ink Jet Head

First, a substrate 1 as shown in FIG. 1 was prepared. A siliconsubstrate is most generally applicable to the substrate 1. In general, adriver, a logic circuit, or the like for controlling a discharge energygenerating element is produced according to a general-purposesemiconductor production method, so silicon is preferably applied to thesubstrate. In this example, a silicon substrate having an electrothermalconverting element (a heater composed of HfB₂) as an ink dischargepressure generating element 2 and a laminate film of SiN+Ta (not shown)in an ink flow path and a nozzle formation site was prepared (FIG. 2 ).

Next, a positive type resist layer was formed on the substrate includingthe ink discharge pressure generating element 2, and the whole waspatterned to form an ink flow path pattern. First, the positive typeresist prepared in (2) was applied by means of spin coating, and thewhole was prebaked at 100° C. for 3 minutes. After that, in a nitrogenatmosphere, the resultant was subjected to a heat treatment in an ovenat 150° C. for 30 minutes. A layer 3 of a photosensitive resincomposition according to the present invention after the heat treatmenthad a thickness of 8 ′μm (FIG. 3).

Subsequently, by means of a Deep-UV exposing device UX-3000 manufacturedby USHIO INC., the resultant was exposed to light having a wavelength of220 to 280 nm at an amount of exposure of 200 mJ/cm². Then, theresultant was subjected to PEB at 120° C. for 180 seconds by means of ahot plate. After that, the resultant was developed with a developercomposed of the following composition to form a flow path pattern 4(FIG. 4). Diethylene glycol monobutyl ether: 60 vol % Ethanolamine:  5vol % Morpholine: 20 vol % Ion-exchanged water: 15 vol %

Next, a negative type photosensitive resin composition composed of thefollowing composition was applied by means of spin coating to thesubstrate to be treated (a thickness of 15 μm on a plate), and the wholewas prebaked at 100° C. for 2 minutes (hot plate) to form a nozzleconstitution member 5 (FIG. 5). EHPE (manufactured by Daicel Chemical100 parts by weight Industries, Ltd.): 1,4HFAB (manufactured by CentralGlass Co.,  20 parts by weight Ltd.): SP-170 (manufactured by ASAHIDENKA Co.,  2 parts by weight Ltd.): A-187 (manufactured by NihonUnicar):  5 parts by weight Methyl isobutyl ketone: 100 parts by weightDiglyme: 100 parts by weight

Next, a photosensitive resin composition composed of the followingcomposition was applied by means of spin coating to the substrate to betreated so as to have a thickness of 1 μm, and the whole was prebaked at80° C. for 3 minutes (hot plate) to form an ink repellent agent layer 6(FIG. 6). EHPE-3158 (manufactured by Daicel Chemical 35 parts by weightIndustries, Ltd.): 2,2-bis (4-glycidyloxyphenyl)hexaphloropropane: 25parts by weight 1,4-bis (2-hydroxyhexaphloroisopropyl) benzene: 25 partsby weight 3-(2-perfluorohexyl) ethoxy-1,2-epoxypropane: 16 parts byweight A-187 (manufactured by Nihon Unicar):  4 parts by weight SP-170(manufactured by ASAHI DENKA Co.,  2 parts by weight Ltd.): Diethyleneglycol monoethyl ether: 100 parts by weight 

Subsequently, by means of an MPA-600 (manufactured by CANON INC.), theresultant was exposed to light having a wavelength of 290 to 400 nm atan amount of exposure of 400 mJ/cm². Then, the resultant was subjectedto PEB at 120° C. for 120 seconds by means of a hot plate. After that,the resultant was developed with methyl isobutyl ketone to pattern thenozzle constitution member 5 and the ink repellent agent layer 6,thereby forming an ink discharge port 7 (FIG. 7). In this example, adischarge port pattern of 8 μmΦ was formed.

Next, an etching mask 8 with an opening shape having a width of 1 mm anda length of 10 mm was created by means of a polyetheramide resincomposition (HIMAL manufactured by Hitachi Chemical Co., Ltd.) on therear surface of the substrate to be treated (FIG. 8). Next, thesubstrate to be treated was immersed in a 22-mass % aqueous solution ofTMAH held at 80° C. to perform anisotropic etching of the substrate,thereby forming an ink supply port 9 (FIG. 9). At this time, theanisotropic etching was performed after a protective layer (OBCmanufactured by Tokyo Ohka Kogyo Co., Ltd.: not shown) had been appliedto the ink repellent agent layer 6 for the purpose of protecting the inkrepellent agent layer 6 from an etchant.

Next, the OBC used as the protective layer was dissolved and removed bymeans of xylene, and then the entire surface of the remainder wasexposed to light having a wavelength of 200 to 280 nm at an amount ofexposure of 8,000 mJ/cm² through the nozzle constitution member and theink repellent agent layer to solubilize the flow path pattern 4.Subsequently, the resultant was immersed in methyl lactate while anultrasonic wave was applied to methyl lactate to dissolve and remove theflow path pattern 4, thereby forming an ink flow path 10. Thus, an inkjet head was produced (FIG. 10). The layer of the polyetheramide resincomposition used as the etching mask was removed by dry etching usingoxygen plasma.

The ink jet head thus produced was mounted on a printer, and wasevaluated for discharge and recording. As a result, the ink jet head wascapable of performing good image recording.

EXAMPLE 2

An ink jet head was produced in the same manner as in Example 1 exceptthat a photosensitive resin composition composed of the followingcomposition was used as a positive type resist. The ink jet head wasevaluated for discharge and recording. As a result, the ink jet head wascapable of performing good image recording. The amount of exposurenecessary for patterning the positive type resist was 150 mJ/cm².Radical copolymer of methacrylic anhydride and 30 g methyl methacrylate:[(monomer composition ratio 20/80: molar ratio), weight averagemolecular weight (Mw: in terms of polystyrene) = 28,000, degree ofdispersion (Mw/Mn) = 3.5] Diphenyliodonium antimonate: 0.8 g  (MPI-103manufactured by Midori Kagaku Co., Ltd.) Cyclohexanone: 70 g

EXAMPLE 3

An ink jet head was produced in the same manner as in Example 1 exceptthat: a photosensitive resin composition composed of the followingcomposition was used as a positive type resist; and exposure wasperformed by means of an MPA-600 (manufactured by CANON INC.) at anamount of exposure of 100 mJ/cτn² at the time of patterning. The ink jethead was evaluated for discharge and recording. As a result, the ink jethead was capable of performing good image recording. Radical copolymerof methacrylic anhydride and  30 g methyl methacrylate: [(monomercomposition ratio 10/90: molar ratio), weight average molecular weight(Mw: in terms of polystyrene) = 30,000, degree of dispersion (Mw/Mn) =3.1] SP-172 (manufactured by ASAHI DENKA Co., Ltd.): 2.0 g SP-100(manufactured by ASAHI DENKA Co., Ltd.): 1.0 g Cyclphexanone:  70 g

COMPARATIVE EXAMPLE 1

A flow path pattern 4 was formed in the same manner as in Example 1except that a positive type resist to which triphenylsulfoniumantimonate (TPS-103 manufactured by Midori Kagaku Co., Ltd.) was notadded was used. In this case, an amount of exposure of 40,000 mJ/cm2 wasnecessary for patterning (PEB was not performed in this case)

EXAMPLE 4

(1) Preparation of a Positive Type Resist

30 g of the copolymer prepared in Example 1 were dissolved into 70 g ofcyclohexanone, and 0.9 g of triphenylsulfonium antimonate (TPS-103manufactured by Midori Kagaku Co., Ltd.) was added to and dissolved intothe solution. After that, the solution was filtered through a 0.2-μmmembrane filter to prepare a positive type resist solution.

(2) Production of an Ink Jet Head

First, a substrate 1 as shown in FIG. 11 was prepared. A siliconsubstrate is most generally applicable to the substrate 1. In general, adriver, a logic circuit, or the like for controlling a discharge energygenerating element is produced according to a general-purposesemiconductor production method, so silicon is preferably applied to thesubstrate. In this example, a silicon substrate having an electrothermalconverting element (a heater composed of HfB₂) as an ink dischargepressure generating element 2 and a laminate film of SiN+Ta (not shown)in an ink flow path and a nozzle formation site was prepared (FIG. 12).

Next, as shown in FIG. 13, polymethyl isopropenyl ketone (ODURmanufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied as a firstpositive type resist layer 11 by means of spin coating to the substrateincluding the ink discharge pressure generating element 2 (FIG. 12), andthe whole was baked at 150° C. for 3 minutes. The resist layer after thebaking had a thickness of 10 μm.

Next, the positive type resist prepared in (2) was applied as a secondpositive type resist layer 12 by means of spin coating, and the wholewas baked at 150° C. for 6 minutes. The resist layer after the bakinghad a thickness of 5 μm (FIG. 14).

Subsequently, the second positive type resist layer was patterned. Byusing a Deep-UV exposing device UX-3000 manufactured by USHIO INC. as anexposing device, the resultant was subjected to pattern exposure at anamount of exposure of 200 mJ/cm². Then, the resultant was subjected toPEB at 120° c. for 180 seconds by means of a hot plate. After that, theresultant was developed with a developer composed of the samecomposition as that of Example 1 to form a second flow path pattern 13(FIG. 15).

Subsequently, the first positive type resist layer was patterned. Byusing an identical exposing device, the resultant was subjected topattern exposure at an amount of exposure of 23,000 mJ/cm², developedwith methyl isobutyl ketone, and subjected to a rinse treatment withisopropyl alcohol to form a first flow path pattern 14 (FIG. 16).

Next, a negative type photosensitive resin composition composed of thesame composition as that of Example 1 was applied by means of spincoating to the substrate to be treated (a thickness of 20 μm on aplate), and the whole was baked at 100° C. for 2 minutes (hot plate) toform a nozzle constitution member 5 (FIG. 17).

Next, a photosensitive resin composition composed of the samecomposition as that of Example 1 was applied by means of spin coating tothe substrate to be treated so as to have a thickness of 1 μm, and thewhole was baked at 80° C. for 3 minutes (hot plate) to form an inkrepellent agent layer 6 (FIG. 18).

Subsequently, by means of an MPA-600 (manufactured by CANON INC.), theresultant was subjected to pattern exposure at an amount of exposure of400 mJ/cm². Then, the resultant was subjected to PEB at 120° C. for 120seconds by means of a hot plate. After that, the resultant was developedwith methyl isobutyl ketone to pattern the nozzle constitution member 5and the ink repellent agent layer 6, thereby forming an ink dischargeport 7 (FIG. 19). In this example, a discharge port pattern of 10 μmΦwas formed.

Next, an etching mask 8 with an opening shape having a width of 1 mm anda length of 10 mm was created by means of a polyetheramide resincomposition (HIMAL manufactured by Hitachi Chemical Co., Ltd.) on therear surface of the substrate to be treated (FIG. 20). Next, thesubstrate to be treated was immersed in a 22-wt % aqueous solution ofTMAH held at 80° C. to perform anisotropic etching of the substrate,thereby forming an ink supply port 9 (FIG. 21). At this time, theanisotropic etching was performed after a protective layer (OBCmanufactured by Tokyo Ohka Kogyo Co., Ltd.: not shown) had been appliedto the ink repellent agent layer 8 for the purpose of protecting the inkrepellent agent layer 6 from an etchant.

Next, the OBC used as the protective layer was dissolved and removed bymeans of xylene, and then the entire surface of the remainder wasexposed to light at an amount of exposure of 250, 000 mJ/cm² through thenozzle constitution member and the ink repellent agent layer by means ofa Deep-UV exposing device UX-3000 manufactured by USHIO INC. tosolubilize the flow path patterns 13 and 14. Subsequently, the resultantwas immersed in methyl lactate while an ultrasonic wave was applied tomethyl lactate to dissolve and remove the flow path patterns 13 and 14,thereby producing an ink jet head (FIG. 22). The layer of thepolyetheramide resin composition used as the etching mask was removed bydry etching using oxygen plasma.

The ink jet head thus produced was mounted on a printer, and wasevaluated for discharge and recording. As a result, the ink jet head wascapable of performing good image recording.

EXAMPLE 5

An ink jet head was produced in the same manner as in Example 4 exceptthat a positive type resist composed of the same composition as that ofExample 2 was used as a second positive type resist. The ink jet headwas evaluated for discharge and recording. As a result, the ink jet headwas capable of performing good image recording. The amount of exposurenecessary for patterning the positive type resist was 150 mJ/cm².

EXAMPLE 6

An ink jet head was produced in the same manner as in Example 1 exceptthat: a photo-degradable positive type resist composed of the followingcomposition was used as a first positive type resist; and an amount ofexposure at the time of patterning was set to 40,000 mJ/cm². The ink jethead was evaluated for discharge and recording. As a result, the ink jethead was capable of performing good image recording.

Radical copolymer of methyl methacrylate and methacrylic acid

[(monomer composition ratio 90/10: molar ratio), weight averagemolecular weight (Mw: in terms of polystyrene)=120,000, degree ofdispersion (Mw/Mn)=1.8]

COMPARATIVE EXAMPLE 2

A flow path pattern having a two-layer structure was formed in the samemanner as in Example 4 except that a second positive type resist towhich triphenylsulfonium antimonate (TPS-103 manufactured by MidoriKagaku Co., Ltd.) was not added was used. In this case, an amount ofexposure of 20,000 mJ/cm² was necessary for patterning the secondpositive type resist. As a result, a trouble occurred, in which part ofthe first positive type resist layer was developer at the time ofdevelopment of the second positive type resist layer.

EXAMPLE 7

(1) Preparation of a Positive Type Resist

30 g of the resultant copolymer were dissolved into 70 g ofcyclohexanone, and 0.6 g of triphenylsulfonium triphlate (TPS-105manufactured by Midori Kagaku Co., Ltd.) was added to and dissolved intothe solution. After that, the solution was filtered through a 0.2-μmmembrane filter to prepare a positive type resist solution.

(2) Production of an Ink Jet Head

First, a substrate 1 as shown in FIG. 23 was prepared. A siliconsubstrate is most generally applicable to the substrate 1. In general, adriver, a logic circuit, or the like for controlling a discharge energygenerating element is produced according to a general-purposesemiconductor production method, so silicon is preferably applied to thesubstrate. In this example, a silicon substrate having an electrothermalconverting element (a heater composed of HfBo) as an ink dischargepressure generating element 2 and a laminate film of SiN+Ta (not shown)in an ink flow path and a nozzle formation site was prepared (FIG. 24).

Next, as shown in FIG. 25, a positive type resist layer was formed onthe substrate including the ink discharge pressure generating element 2.The above positive type resist was applied by means of spin coating, andthe whole was prebaked at 100° C. for 3 minutes. After that, in anitrogen atmosphere, the resultant was subjected to a heat treatment inan oven at 150° C. for 30 minutes. The resist layer after the heattreatment had a thickness of 10 μM (FIG. 25).

Subsequently, the resultant was exposed to Deep-UV light having awavelength of 200 to 280 nm at an amount of exposure of 400 mJ/cm².Then, the resultant was subjected to PEB at 120° C. for 180 seconds bymeans of a hot plate. After that, the resultant was developed with thesame developer as that of Example 1 to form a first flow path pattern 16(FIG. 26). At this time, the first flow path pattern had a height of 4μm.

Subsequently, the resultant was exposed to Deep-UV light having awavelength of 200 to 280 nm at an amount of exposure of 40,000 mJ/cm².Then, the resultant was developed with the same developer as thatdescribed above to form a second flow path pattern 17 (FIG. 27). Thus,an ink flow path pattern was obtained, which had the first flow pathpattern 16 having a height of 4 μm on the second flow path pattern 17having a height of 6 μm.

Next, a photosensitive resin composition composed of the samecomposition as that of Example 1 was applied by means of spin coating tothe substrate to be treated (a thickness of 15 μm on a plate), and thewhole was baked at 100° C. for 2 minutes (hot plate) to form a nozzleconstitution member 5 (FIG. 28).

Subsequently, a photosensitive resin composition composed of the samecomposition as that of Example 1 was applied by means of spin coating tothe substrate to be treated so as to have a thickness of 1 μm, and thewhole was baked at 80° C. for 3 minutes (hot plate) to form an inkrepellent agent layer 6 (FIG. 29).

Next, by means of an MPA-600 (manufactured by CANON INC.), the resultantwas subjected to pattern exposure with light having a wavelength of 290to 400 nm at an amount of exposure of 400 mJ/cm². Then, the resultantwas subjected to PEB at 90° C. for 120 seconds by means of a hot plate.After that, the resultant was developed with methyl isobutyl ketone topattern the nozzle constitution member 5 and the ink repellent agentlayer β, thereby forming an ink discharge port 7 (FIG. 30). In thisexample, a discharge port pattern of 8 μmΦ was formed.

Next, an etching mask 8 with an opening shape having a width of 1 mm anda length of 10 mm was created by means of a polyetheramide resincomposition (HIMAL manufactured by Hitachi Chemical Co., Ltd.) on therear surface of the substrate to be treated (FIG. 9). Next, thesubstrate to be treated was immersed in a 22-wt % aqueous solution ofTMAH held at 80° C. to perform anisotropic etching of the substrate,thereby forming an ink supply port 9 (FIG. 31). At this time, theanisotropic etching was performed after a protective layer (OBCmanufactured by Tokyo Ohka Kogyo Co., Ltd.: not shown) had been appliedto the ink repellent agent layer 6 for the purpose of protecting the inkrepellent agent layer 6 from an etchant.

Next, the OBC used as the protective layer was dissolved and removed bymeans of xylene, and then the entire surface of the remainder wasexposed to light having a wavelength of 200 to 280 nm at an amount ofexposure of 80,000 mJ/cm² through the nozzle constitution member and theink repellent agent layer to solubilize the ink flow path pattern.Subsequently, the resultant was immersed in methyl lactate while anultrasonic wave was applied to methyl lactate to dissolve and remove theink flow path pattern, thereby producing an ink jet head (FIG. 33). Thelayer of the polyetheramide resin composition used as the etching maskwas removed by dry etching using oxygen plasma.

The ink jet head thus produced was mounted on a printer, and wasevaluated for discharge and recording. As a result, the ink jet head wascapable of performing good image recording.

EXAMPLE 8

An ink jet head was produced in the same manner as in Example 7 exceptthat: a photosensitive resin composition composed of the followingcomposition was used as a positive type resist; a reaction for makingpositive derived from hydrolysis was allowed to correspond to an i line;and exposure was performed by means of an i line stepper (manufacturedby CANON INC.: FPA-3000iW) at an amount of exposure of 1,000 J/m² at thetime of patterning in the first photolithographic step. The ink jet headwas evaluated for discharge and recording. As a result, the ink jet headwas capable of performing good image recording. The first flow pathpattern 16 formed at this time had a height of 5 μm. Radical copolymerof methacrylic anhydride and 30 g methyl methacrylate: (same as that ofExample 7) SP-172 (manufactured by ASAHI DENKA Co., Ltd.): 2.0 g SP-100(manufactured by ASAHI DENKA Co., Ltd.): 1.0 g Cyclohexanone:  70 g

EXAMPLE 9

An ink jet head was produced in the same manner as in Example 7 exceptthat: a photosensitive resin composition composed of the followingcomposition was used as a positive type resist; and PEB was performed at110° C. for 180 seconds at the time of patterning in the firstphotolithographic step. The ink jet head was evaluated for discharge andrecording. As a result, the ink jet head was capable of performing goodimage recording. The first flow path pattern 16 formed at this time hada height of 4 μm. Radical copolymer of methacrylic anhydride and 30 gmethyl methacrylate: (same as that of Example 7) TPS-105 (manufacturedby Midori Kagaku Co., 0.9 g Ltd.): Cyclohexanone:  70 g

This application claims priority from Japanese Patent Application No.2004-190479 filed on Jun. 28, 2004, which is hereby incorporated byreference herein.

1. A positive type photosensitive resin composition, comprising atleast: (1) an acrylic resin having a carboxylic anhydride structure in amolecule; and (2) a compound that generates an acid when irradiated withlight.
 2. A photosensitive resin composition according to claim 1,wherein the acrylic resin undergoes intramolecular cross-linking throughthe carboxylic anhydride structure.
 3. A photosensitive resincomposition according to claim 1, wherein the acrylic resin has thecarboxylic anhydride structure at a side chain thereof.
 4. Aphotosensitive resin composition according to claim 1, wherein theacrylic resin has at least one kind of structural units represented bythe following general formulae 1 and
 2.

(In the general formulae 1 and 2, Ri to R₄ each independently representa hydrogen atom or an alkyl group having 1 to 3 carbon atoms.)
 5. Aphotosensitive resin composition according to claim 1, wherein theacrylic resin comprises a polymer containing at least methacrylicanhydride as a monomer component. β. A photosensitive resin compositionaccording to claim 1, wherein the acrylic resin comprises a polymercontaining at least methacrylic anhydride and methyl methacrylate asmonomer components.
 7. A photosensitive resin composition according toclaim 1, wherein the compound that generates an acid when irradiatedwith light comprises one of an aromatic sulfonium salt, an aromaticiodonium salt, and a triazine compound.
 8. A method of forming a patternhaving a level difference on a substrate by means of a positive typephotosensitive resin, comprising: (1) a step of forming a layer of thephotosensitive resin composition according to claim 1 on the substrate;(2) a first photolithographic step of removing a part except a partserving as a first pattern of the layer of the photosensitive resincomposition up to a predetermined depth in a thickness direction to formthe first pattern composed of a part protruding from the predetermineddepth; and (3) a second photolithographic step of removing a part on thesubstrate except a part serving as a second pattern of the layer of thephotosensitive resin composition on which the first pattern is formedwhile maintaining a shape of the first pattern to prepare a patternhaving a level difference shape in which the first pattern is placed onthe second pattern, characterized in that: the first lithography stepincludes process steps of exposure, heating after exposure, anddevelopment; a reaction for making the layer of the photosensitive resincomposition positive in the first photolithographic step is derived fromat least a hydrolytic reaction of a carboxylic anhydride in the acrylicresin; the second photolithographic step includes process steps ofexposure and development; and a reaction for making the layer of thephotosensitive resin composition positive in the secondphotolithographic step is derived from at least a main chaindecomposition reaction of the acrylic resin.
 9. A method of forming alevel difference pattern according to claim 8, wherein an exposurewavelength in the first photolithographic step is longer than anexposure wavelength in the second photolithographic step.
 10. A methodof forming a level difference pattern according to claim 8, wherein adeveloper containing: (1) a glycol ether which can be mixed with waterat an arbitrary ratio and has 6 or more carbon atoms; (2) anitrogen-containing basic organic solvent; and (3) water is used as adeveloper for the positive type photosensitive resin.
 11. A method offorming a level difference pattern according to claim 10, wherein theglycol ether comprises at least one kind of ethylene glycol monobutylether and diethylene glycol monobutyl ether.
 12. A method of forming alevel difference pattern according to claim 10, wherein thenitrogen-containing basic organic solvent comprises at least one kind ofethanolamine and morpholine.
 13. A method of producing an ink jet headincluding: a discharge port for discharging ink; an ink flow path whichis in communication with the discharge port and has therein a pressuregenerating element for discharging the ink; a substrate on which thepressure generating element is formed; and an ink flow path formingmember which is joined to the substrate to form the ink flow path, themethod comprising the steps of: (1) arranging a layer of a positive typephotosensitive resin composition on the substrate on which the pressuregenerating element is formed; (2) irradiating a predetermined site ofthe layer of the photosensitive resin composition with ionizationradiation; (3) removing the site irradiated with the ionizationradiation through development to form a desired ink flow path pattern;(4) forming, on the ink flow path pattern, a coating resin layer forforming an ink flow path wall; (5) forming, in the coating resin layerplaced on the pressure generating element formed on the substrate, anink discharge port; and (6) dissolving and removing the ink flow pathpattern, characterized in that the positive type photosensitive resincomposition comprises the photosensitive resin composition according toclaim
 1. 14. A method of producing an ink jet head including: adischarge port for discharging ink; an ink flow path which is incommunication with the discharge port and has therein a pressuregenerating element for discharging the ink; a substrate on which thepressure generating element is formed; and an ink flow path formingmember which is joined to the substrate to form the ink flow path, themethod comprising the steps of: (1) arranging a layer of a firstpositive type photosensitive resin composition on the substrate on whichthe pressure generating element is formed; (2) forming a layer of asecond positive type photosensitive resin composition on the layer ofthe first positive type photosensitive resin composition; (3)irradiating a predetermined site of the layer of the second positivetype photosensitive resin composition with ionization radiation having awavelength region in which the layer of the second positive typephotosensitive resin composition can react; (4) removing the site of thelayer of the second positive type photosensitive resin compositionirradiated with the ionization radiation through development to form asecond ink flow path pattern; (5) irradiating a predetermined site ofthe layer of the first positive type photosensitive resin compositionwith ionization radiation having a wavelength region in which the layerof the first positive type photosensitive resin composition can react;(6) removing the site of the layer of the first positive typephotosensitive resin composition irradiated with the ionizationradiation through development to form a first ink flow path pattern; (7)forming, on the first and second ink flow path patterns, a coating resinlayer for forming an ink flow path wall; (8) forming, in the coatingresin layer placed on the pressure generating element formed on thesubstrate, an ink discharge port; and (9) dissolving and removing thefirst and second ink flow path patterns, characterized in that thesecond positive type photosensitive resin composition comprises thephotosensitive resin composition according to claim
 1. 15. A method ofproducing an ink jet head including: a discharge port for dischargingink; an ink flow path which is in communication with the discharge portand has therein a pressure generating element for discharging the ink; asubstrate on which the pressure generating element is formed; and an inkflow path forming member which is joined to the substrate to form theink flow path, the method comprising: (1) a step of forming a layer ofthe photosensitive resin composition according to claim 1 on thesubstrate on which the pressure generating element is formed; (2) afirst photolithographic step of removing a part except a part serving asa first ink flow path pattern of the layer of the photosensitive resincomposition up to a predetermined depth in a thickness direction to formthe first ink flow path pattern composed of a part protruding from thepredetermined depth; (3) a second photolithographic step of removing apart on the substrate except a part serving as a second ink flow pathpattern of the layer of the photosensitive resin composition on whichthe first ink flow path pattern is formed while maintaining a shape ofthe first ink flow path pattern to prepare a level difference structurein which the first ink flow path pattern is placed on the second inkflow path pattern; (4) a step of forming, on the level differencestructure, a coating resin layer for forming an ink flow path wall; (5)a step of forming, in the coating resin layer placed on the pressuregenerating element formed on the substrate, an ink discharge port; and(6) a step of dissolving and removing the level difference structure,characterized in that: the first lithography step includes process stepsof exposure, heating after exposure, and development; a reaction formaking the layer of the photosensitive resin composition positive in thefirst photolithographic step is derived from at least a hydrolyticreaction of a carboxylic anhydride in the acrylic resin; the secondphotolithographic step includes process steps of exposure anddevelopment; and a reaction for making the layer of the photosensitiveresin composition positive in the second photolithographic step isderived from at least a main chain decomposition reaction of the acrylicresin.
 16. A method of producing an ink jet head according to claim 15,wherein an exposure wavelength in the first photolithographic step islonger than an exposure wavelength in the second photolithographic step.17. A method of producing an ink jet head according to claim 15, whereina developer containing: (1) a glycol ether which can be mixed with waterat an arbitrary ratio and has 6 or more carbon atoms; (2) anitrogen-containing basic organic solvent; and (3) water is used as adeveloper for the positive type photosensitive resin.
 18. A method ofproducing an ink jet head according to claim 17, wherein the glycolether comprises at least one kind of ethylene glycol monobutyl ether anddiethylene glycol monobutyl ether,
 19. A method of producing an ink jethead according to claim 17, wherein the nitrogen-containing basicorganic solvent comprises at least one kind of ethanolamine andmorpholine.
 20. An ink jet head produced according to the method ofproducing an ink jet head according to claim 13.